The present invention relates to a novel organopolysiloxane compound or, more particularly, to an organopolysiloxane compound capable of exhibiting a liquid-crystalline phase in a crosslinked condition so as to be useful as a material for a display unit in electronic instruments or as a material of temperature sensor.
As is well known, a liquid crystal is a material simultaneously having electrical or optical anisotropy inherent in solids and fluidity inherent in liquids and is used as a material for optoelectronic devices or display units, material of temperature sensors, filling material of columns and the like.
Known liquid-crystal materials used in these applications include low-molecular as well as high-polymeric compounds. The high-polymeric liquid-crystal materials include main chain-type all-aromatic polyesters and side chain-type polyacrylic and polymethacrylic esters and polysiloxanes, of which those of the polysiloxane type are preferred in respect to their excellent low-temperature characteristics and weatherability.
The polysiloxane-type liquid-crystalline materials known in the prior art are mostly a liquid organopolysiloxane having a linear molecular structure to which mesogen residues are grafted. Besides, Japanese Patent Kokai No. 58-17119 discloses a linear organopolysiloxane having a crosslinkable structure by which the compound is crosslinked to lose fluidity but still retains a liquid-crystalline phase. In an example disclosed in this patent document, a mixture composed of an organohydrogenpolysiloxane, vinyl-substituted mesogen compound and organopolysiloxane having a silicon-bonded vinyl group at each molecular chain end as a crosslinking agent is subjected to the addition reaction between the silicon-bonded hydrogen atoms and the silicon-bonded vinyl groups so as to simultaneously effect the grafting reaction of the mesogen molecules and the crosslinking reaction of the organopolysiloxane so that the reaction product is a crosslinked organopolysiloxane capable of exhibiting a liquid-crystalline phase. The liquid-crystalline material of this type has several disadvantages. The degree of crosslinking cannot be sufficiently high because the cross-linking agent is difunctional, that the material is not stable even in a sealed condition when a catalyst for the crosslinking reaction is admixed therewith and that the crosslinking reaction cannot proceed at a practical velocity unless the composition is heated.
Alternatively, Japanese Patent Kokai Nos. 58-17119 and 62-30123 propose a compound, which is non-liquid but liquid-crystalline, obtained by the crosslinking reaction of a silane or a mixture of silanes represented by the general formula R.sub.m SiR'.sub.4-m, in which R is a mesogen residue, R' is a group capable of pertaining to the condensation reaction and m is zero, 1, 2 or 3, in the presence of a condensation catalyst. This organopolysiloxane, however, cannot exhibit the low-temperature characteristics inherent in the siloxane linkages because of the relatively small content of the linear segments in the molecules of this compound.